Description:
------------
When passing an argument to a function such as: -

  preg_match( string pattern, string subject [, array &matches [, int flags [, int offset]]] )

using the syntax:

  preg_match($pattern, $subject, $array = array())

a copy of the $array is passed to the function, rather than a pointer.

Reproduce code:
---------------
// Without first defining variable
preg_match("/a/", "a", $matches1);
echo count($matches1); // Outputs 1 - OK

// Defining variable before function call
$matches2 = array();
preg_match("/a/", "a", $matches2);
echo count($matches2); // Outputs 1 - OK

// Defining variable within function parameters
preg_match("/a/", "a", $matches3 = array());
echo count($matches3); // Outputs 0 - UNEXPECTED!!



Expected result:
----------------
Expected result: 111


Actual result:
--------------
Observed result: 110

Further toying around, such as by using: -

function _array() 
{
  $a = array('a', 'b', 'c');
}

instead of array() and 

function _preg_match($pattern, $subject, &$matches)
{
  if (!$matches) 
  {
    $digits = array();
  }
  echo "in: " . count($matches) ."<br/>\n";
  $result = preg_match($pattern, $subject, $matches);
  echo "out: " . count($matches) ."<br/>\n";
  return $result;
}

instead of preg_match(), reveal that the array is being passed by copy, not reference.